Wang Jiankang (right), who is Ling Jihua's (left) brother-in-law and a deputy mayor in Yuncheng in Shanxi province, has been in custody for more than 10 days.

The detention of a relative of Ling Jihua, a former senior aide to ex-president Hu Jintao, has led to speculation the authorities may be building a case against Ling himself.

Wang Jiankang, who is Ling's brother-in-law and a deputy mayor in Yuncheng in Shanxi province, has been in custody for more than 10 days.

He is either helping with, or is directly implicated in a corruption inquiry, three sources told the South China Morning Post.

Wang is the latest relative of Ling - currently a vice-chairman of the country's top political advisory body, the Chinese People's Political Consultative Conference (CPPCC) - to be detained.

Last month, Ling's brother Ling Zhengce was taken into custody over allegations of corruption. He is a vice-chairman of the Shanxi CPPCC.

Zhang Lifan, a Beijing-based political analyst, said: "If the party is examining Wang Jiankang, it could suggest an investigation into Ling Jihua is on the way, especially after the earlier detention of his brother Ling Zhengce. It has been common practice for the party to clean up the surrounding underlings when deciding to investigate someone at the top."

One of the sources said Wang's wife, Ling's elder sister Ling Luxian, had also been detained.

"I was told the initial interrogation of Wang was triggered by an allegation of embezzlement," the source added.

Ling Jihua, Hu's former personal secretary, was seen as a rising star because of his close relationship to the ex-president.

But his career suffered after allegations that he tried to cover up details of his son's death in March 2012.

The son, Ling Gu, died after the Ferrari he was driving crashed in Beijing. Two women in the car were seriously injured.

Ling Jihua failed to win promotion to the Politburo later that year in the wake of the scandal. After the publicity surrounding his son's death, he transferred to lead the Communist Party's ceremonial United Front Work department.

He was later appointed a vice-chairman of the CPPCC.

Ling Jihua comes from Shanxi and was said to be a founder of the "Shanxi gang", officials who either worked their way up the ranks in the coal-rich province or traced their ancestry to there.

Several senior officials with links to the province have been detained over allegations of corruption this year.

They include Xie Kemin, the former deputy head of the province's anti-corruption bureau, who was thrown out of the Communist Party earlier this month for graft.

Two sources said Wang, 55, a former mechanic who became a deputy mayor of Yuncheng in 2009, disappeared from public view more than a week ago.

His last public appearance was at a June 26 meeting discussing a water management project, according to the local official newspaper Yuncheng Daily.

"Wang Jiankang has asked for leave," said a staff member at his government office in Yuncheng yesterday, declining to give further information.

This article appeared in the South China Morning Post print edition as Former Hu aide 'could be target of graft probe'